The Viscount of Shadows. The Rakes of St. Regent's Park, #6

Oliver Wollstonecraft, Viscount Tensbridge and recent member of The Rakes of St. Regent's Park, has a secret: he leads a double life. He sits on a progressive parliamentary committee by day, crafting laws to benefit the less fortunate. But by night, Oliver tests those values, acting as The Sentinel, a masked protector of the underprivileged. Nothing shakes his stoic resolve until he comes to the aid of a bold and fiery woman who turns out to be a lady detective.
She awakens emotions Oliver believed were well hidden. Claudia Ellingford has secrets of her own. The illegitimate daughter of a villainous duke, she spent the past ten years surviving on the streets. Recently hired by The Galway Investigative Agency, Claudia relishes her exciting new occupation. But nothing prepared her for seeing a masked man lurking in the shadows and patrolling the alleys of a notorious section of London.
What is more shocking is that the stuffy viscount who hired her is the vigilante that stirred her dormant desire. Claudia and Oliver become swept up into a perilous situation, with a vicious criminal determined to discover The Sentinel's true identity. But what is also in danger is their hearts, facing their doubts, and finding a path to lasting happiness.